Method for forcing fluent material into a substantially restricted zone

ABSTRACT

Fluent material is forced into a substantially restricted zone of utilization, having one irregular surface, for example, in impregnating an epoxy material between a number of helically wound strands on a mandrel closely surrounded by a tubular member, as in the forming of a waveguide. A first, holding pressure above atmospheric is applied to the fluent material to prevent back flow while a succession of pressure pulses at a second, increased pressure is introduced into the fluent material to drive the material into the substantially restricted zone at an increased rate of flow and effect uniform impregnation. A reciprocating pump may be utilized to provide the pulses of pressure at the second, increased pressure, while a check valve may be set to provide the first, holding pressure in the fluent material.

United States Patent Ramachandran Oct. 16, 1973 [75] inventor: Karapurath Ramachandran,

Hightstown, NJ.

[73] Assignee: Western Electric Company, New

York, NY.

[22] Filed: Aug. 11, 1971 [21] Appl. No.: 170,766

[52] US. Cl ..ll7/65.2,117/113,117/161ZB, 1l6/D1G. 2, 156/173, 156/285, 156/305, 156/312 [51] Int. Cl 844d 1/06 B44d/1/44, B65h/81/00 [58] Field of Search l17/65.2, 1612B, 117/116, 113; 156/173, 285, 305, 312

[56] References Cited UNITED STATES PATENTS 3,336,175 8/1967 Nutt et al 156/173 3,664,859 5/1972 Beatty et al,... l17/46 3,671,299 6/1972 Barnett 117/147 3,677,805 7/1972 Barnett... 117/147 3,273,226 9/1966 Brous et a1 29/1555 3,336,176 8/1967 Mednet 156/173 AlR RECIPROCATING PUMP AIR HYDRAULlC RESERVOIR 3,505,102 4/1970 Meam et a1. 117/147 3,566,316 2/1971 Sawada et al 333/95 3,467,546 9/1969 Page et a1. 117/116 3,632,409 11/1972 Barnett 117/116 Primary ExaminerWil1iam D. Martin Assistant ExaminerM. Sofocleous Attorney-Jack Schuman 5 7] ABSTRACT Fluent material is forced into a substantially restricted zone of utilization, having one irregular surface, for example, inimpregnating an epoxy material between a number of helically wound strands on a mandrel closely surrounded by a tubular member, as in the forming of a waveguide. A first, holding pressure above atmospheric is applied to the fluent material to prevent back flow while a succession of pressure pulses'at a second, increased pressure is introduced into the fluent material to drive the material into the substantially restricted zone at an increased rate of flow and effect uniform impregnation. A reciprocating pump may be utilized to provide the pulses of pressure at the second, increased pressure, while a check valve may be set to provide the first, holding pressure in the fluent material.

3 Claims, 2 Drawing Figures EVACUATED WAVEGUI D F.

MANDREL WITH wmomc FREE FLOATING PISTON we n J HYDRAULIC EPOXY FLUID PATENTEUHET I8 I915 .765.926

HRECIPROCATING ,l4

PUMP

AIR HYDRAULIC EVACUATED WAVEGUIDE MANDREL I WITH WINDING REsERvOIR FREE FLOATING PISTON 27 9x I mg? L- I A ZI/ 3 HYDRAULIC EPOXY FLUID PRESSURE VARIATION WITH TIME 2 I PREssuRE ON EPOXY TIME J/I/VE'NTLIJFP METHOD FOR FORCING FLUENT MATERIAL INTO A SUBSTANTIALLY RESTRICTED ZONE BACKGROUND OF THE INVENTION This invention relates to methods and apparatus for forcing a fluent material into a substantially restricted zone of utilization and, more particularly, to the forming of helix waveguide sections in which a fluent material is impregnated between helical windings of one or more strands surrounding a mandrel, the wound mandrel being located within the bore of a tubular member.

In the art of forcing a fluent material into a substantially restricted zone of utilization, it is known to apply a constant pressure of a given magnitude to a quantity of the fluent material in fluid communication with the substantially restricted zone. Such method, while simple and fairly reliable, requires the use of relatively high impregnation pressures in order to drive the fluent material into all portions of the substantially restricted area. The known method is also relatively slow to perform, a clearly undesirable aspect from a production use standpoint.

With particular reference to the forming of sections of helix waveguide for use in millimeter wave transmission systems, it is necessary to impregnate a fluent epoxy material into the coils of wires wound helically about a mandrel with the mandrel disposed within the bore of a tube section. Constant pressure impregnation, as for example in W. G. Nutt et al. U. S. Pat. No. 3,336,175 issued Aug. 15, 1967, has been found unduly slow and has, moreover, required unduly high impregnation pressures to fill the annular space between the tube and the wound helix with the fluent epoxy material and also force the material between the helix windings. Clearly, a faster, lower pressure method and apparatus would be most desirable.

SUMMARY OF THE INVENTION An object of theinvention resides in new and improved methods and apparatus for forcing a fluent material into a substantially restricted zone defined by at least one irregular surface.

The invention contemplates the continuous application of the fluent material to one end of the substantially restricted zone at a first pressure above atmospheric to prevent back flow of the material out-of the zone, while introducing into the fluent material a succession of pulses of pressure at a second pressure greater than the first pressure to drive the fluent material into the substantially restricted zone at an increased rate of flow. The second pressure is still well below that required for steady-state impregnation under otherwise similar conditions.

The method of the invention may be accomplished by apparatus which incorporates a reciprocating pump v for producing the second, higher pressure. The first, lower, holding pressure may be provided, upon .the

' completion of a first pressure stroke of the reciprocatto force a globule of the fluent epoxy material between the coils of the helically wound wires. Cyclic relax- BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the drawing is a schematic illustration of apparatus which may be used in accordance with the principles of the invention for forcing a fluent material into a substantially restricted zone of utilization; and

FIG. 2 is a generalized plot of pressure in the fluent material versus time, depicting the manner in which pressure is built up in the fluent material through utilization of the apparatus of FIG. 1 to carry out the method of the invention.

DETAILED DESCRIPTION Referring to FIG. 1 of the drawing, it is desired to introduce a fluent material 11, such as an epoxy, into a substantially restricted zone of utilization 12. The substantially restricted zone 12 is formed between an inner wall of-a tubular member 13, which may be made of steel, and a mandrel 14 which may carry a number of helically wound conductive and/or dielectric strands,- e.g., copper wires and fiberglass strands. A suitable fluent epoxy material 11 may be formulated by a mixture of twenty-five parts of a resin designated by the trademark Epon 815" which may be obtained from Miller- Stephenson Chemical Company, Inc. of Danbury, Connecticut; four parts of an Epon Z curing agent obtainable from the same company; 25 parts of Velveteen R silica, which may be obtained from Tamms Industries of Cossoplis, Michigan; and two parts of Versamid polyamide resin Number from General Mills Chemicals, Inc. of Kankakee, Illinois. The fluent epoxy material 11 is to impregnate the helical windings which surround the mandrel. After curing of the epoxy, the mandrel l4, wich was previously coated with a mold release material, is to be withdrawn from the tubular member 13, leaving the helical windings adhering to the inner wall of the tubular member at fixed spacings between adjacent helix convolutions. The resultant structure is useful as a medium for transmitting waves of millimeter wavelength. 1

A charging reservoir-l6 takes the form of a horizontally disposed cylinder surrounding a free-floating piston 17. The piston 17 divides the charging reservoir into a first chamber 18 for containing the fluent epoxy impregnating material 11 and a second chamber 19 for admitting a hydraulic working fluid 21. A fluid line 22 runs from the first chamber 18 to the substantially restricted zone 12 between the helically wound mandrel 14 and the tubular member 13. The tubular member is sealed at both its ends 23 and 24, with provision made for the fluid line 22 to communicate with the substantially restricted zone 12 through tube end 24.

-A reciprocating, air-hydraulic pump 26 is utilized to deliver the hydraulic working fluid 21 from a working fluid reservoir 27 to a fluid line 28. The fluid line 28,

which contains a check valve 29, communicates with the second chamber 19 of the cylindrical charging reservoir 16 for introducing into the second chamber pressurized working fluid to operate on the piston 17. The check valve 29 is set to maintain in the line 28 a first, holding pressure intermediate atmospheric pressure and a second, elevated pressure within the capacity of the reciprocating pump 26.

A method of forcing the fluent epoxy material 11 into the substantially restricted zone 12, utilizing the apparatus illustrated schematically in FIG. 1, will next be described, with reference also to FIG. 2 of the drawing. The generalized pressure versus time plot of FIG. 2 indicates the pressure condition in the fluent epoxy material 1 1 during the performance of the method, pressure p corresponding to the first, holding pressure and pressure p, to the second, elevated pressure, greater than p and within the capacity of the reciprocating pump 26, as outlined previously.

According to the practice of the method, a first, holding pressure p above atmospheric is continuously applied to the fluent epoxy material 11 to force the fluent material continuously toward the substantially restricted zone 12 and prevent back flow of the material out of the substantially restricted zone. This first pressure p, is provided by the operation of the check 'valve 29 on the working fluid 21 in the fluid line 28 after a first stroke of the reciprocating pump 26 builds up pressure in the line 28 to above the level of the first, holding pressure. The pressure maintained in the working fluid 21 is communicated to the fluent material 11 by action of the free-floating piston 17 within the cylindrical charging reservoir 16.

Simultaneously with the continuous application of the first, holding pressure p to the fluent material 11, there is introduced into the fluent material, a succession of intermittent pulses of pressure at an elevated, second pressure p greater than the first pressure p The pressure pulses may occur once every few seconds. The pulses serve to drive globules of the fluent material into the substantially restricted zone 12 at an increased rate of flow and to impregnate the material uniformly between the helical coils on the mandrel 14. The intermittent pulses of pressure at the second pressure p over the first, holding pressure are provided by the action of the reciprocating pump 26 on the working fluid 21 in the fluid line 28. Once again, the pressure effect is communicated to the fluent material 11 by operation of the piston 17 in the cylindrical reservoir 16. A valve 31 in a fluid by-pass line 32 between the fluid line 28 and the working fluid reservoir 27 may be manipulated, with the aid ofa pressure gauge 33 communicating with line 28 preferably upstream of the check valve 29, to regulate the second pressure p to any desired value, greater than the first pressure p,, within the capacity of the reciprocating'pump 26.

As can be seen in FIG. 2, with each pressure stroke of the reciprocating pump 26 the pressure in the fluid line 28 will correspond to the elevated, second pressure p, set by the valve 31. Initially, the pressure in line 28 between pressure strokes of the reciprocating pump will drop to the first, holding pressure p Each drop in pressure in the line 28, which may be read on a pressure gauge 34 positioned downstream of the check valve 29, indicates that a quantity of the fluent epoxy material 11 has been driven into the substantially 'restricted zone 12, presumably along thepath of least resistance provided by the annular space between the tubular member 13 and the helically wound mandrel 14. Pressure impulsing to the second 1 pressure p overcomes the resistance of the wound helix structure and impregnates each successive globule of the fluent material between the windings. Helix impregnation is believed aided by a cyclical relaxation in the windings between the pressure pulses, opening more widely the zone between adjacent windings into which each subsequent increased pressure pulse will then force an additional globule of the material. A succession of intermittent pressure pulses, as would initially be observed on the gauge 33. is depicted in the left half of the plot of FIG. 2.

Eventually, successive pressure drops sensed by the pressure gauge 34 will begin to decrease as impregnation of the fluent epoxy material 11 into the substantially restricted zone 12 continues. Finally, a continuous pressure reading correspnding to the elevated, second pressure p will be observed, indicating that the helical windings have been saturated with the fluent material, completing the impregnation process. A valve 36 may now be closed to retain the fluent epoxy material within the tubular member 13 during subsequent cur ing operations. Meanwhile, the pressurization of the charging reservoir 16 by action of the reciprocating pump 26 may be terminated and a valve 37 opened to release the pressurized working fluid 21 back into the working fluid reservoir 27.

In a specific example of the method described above, five meter long helix waveguide sections of a 51 millimeter inner diameter were formed through impregnation of copper wires wound about a mandrel 14 located within each tubular member 13. The fluent epoxy material 11 described above was employed. First and second pressures of about 700 psi and about 1,300 psi, respectively, were utilized, pulses of pressure at the elevated second pressure occurring once every approximately four seconds. Complete impregnation occurred in about fifteen minutes. Under similar conditions, steady-state impregnation at a constant pressure of approximately 2,500 psi has been found necessary to produce a like product, the steady-state process taking much longer than fifteen minutes to complete.

It is to be understood that the described method and apparatus are simply illustrative of one embodiment of the invention. Clearly, numerous modifications are possible. For example, the air-hydraulic reciprocating pump 26 might be replaced by a single fluid reciprocating pump which operates directly on any suitable working fluid 21, e.g., compressed air or a hydraulic fluid. Indeed, the reciprocating pump 26 or any other pressure pulsing mechanism might operate directly on the fluent material 11 without the use of the intermediate charging reservoir 16. In another embodiment, the check valve 29 might be replaced by any other device for maintaining the constant holding pressure p and/or might be positioned in the fluid line 22 between the cylindrical charging reservoir 16 and the substantially restricted zone 12. Many additional modifications may be made in accordance with the principles of the invention.

What is claimed is:

1. In a method of impregnating a helical winding on a helieally wound mandrel by forcing a fluent epoxy impregnating material about and between the strands of the winding while the wound mandrel is disposed closely surrounded by a tubular member wherein the fluent epoxy impregnating material is continuously applied at a first pressure above atmospheric to an end of the tubular member to urge the said fluent epoxy impregnating material between the tubular member and the mandrel and prevent back flow of the fluent epoxy impregnating material away from the helical winding, the improvement which comprises subjecting the fluent epoxy impregnating material to a succession of intermittent pulses of second pressure greater than said first pressure to drive the fluent epoxy impregnating material between the strands ofthe helical winding.

2. The method of claim 1, further comprising: continually measuring the pressure level in the fluent epoxy impregnating material during a succession of pulses at said second pressure until substantially no decrease in pressure is measured at the end of a pulse, which event is indicative of the saturation of the helical winding with the fluent epoxy impregnating material, and

terminating the application of pressure pulses to the fluent epoxy impregnating material upon the occurrence of said event indicating saturation.

3. In a process for constructing a waveguide comprising an inner layer of helically wound strands within a tubular rigid jacket, wherein a mandrel having said strands helically wound thereon is inserted within and closely adjacent to the tubular jacket and an epoxy coating material is applied to one end of the space between the mandrel and the tubular jacket at a first pressure greater than atmospheric, the improvement which comprises subjecting the epoxy material to a succession of pulses at a second higher pressure until substantially no decrease in pressure is observed at the end of one of said pulses. 

2. The method of claim 1, further comprising: continually measuring the pressure level in the fluent epoxy impregnating material during a succession of pulses at said second pressure until substantially no decrease in pressure is measured at the end of a pulse, which event is indicative of the saturation of the helical winding with the fluent epoxy impregnating material, and terminating the application of pressure pulses to the fluent epoxy impregnating material upon the occurrence of said event indicating saturation.
 3. In a process for constructing a waveguide comprising an inner layer of helically wound strands within a tubular rigid jacket, wherein a mandrel having said strands helically wound thereon is inserted within and closely adjacent to the tubular jacket and an epoxy coating material is applied to one end of the space between the mandrel and the tubular jacket at a first pressure greater than atmospheric, the improvement which comprises subjecting the epoxy material to a succession of pulses at a second higher pressure until substantially no decrease in pressure is observed at the end of one of said pulses. 